1. Field of the Invention
The invention relates to thermal printing techniques, and more particularly, to thermal printing apparatus and printing methods thereof.
2. Description of the Prior Art
In general, image printing techniques can be classified into four major categories: dot matrix printing technique, inkjet printing technique, laser printing technique, and thermal printing technique. The thermal printing technique can be classified into two categories of direct thermal printing technique and thermal transfer printing technique, wherein the thermal transfer printing technique includes thermal sublimation printing technique and thermal wax printing technique. Taking the thermal transfer printing technique as an example, the thermal transfer printing technique has a better output image quality than other printing techniques due to the fact that the thermal transfer printing technique can possess continuous tone printing performance. It is well known that the thermal transfer printer utilizes a thermal print head to heat ribbons containing dyes in order to transfer the dyes onto an object to be printed. In this way, continuous-tone can be formed on the object according to the heating time or the heating temperature.
In the conventional techniques, if the thermal transfer printer is required to output an image having 256 color levels, a controlling circuit of the thermal transfer printer has to transfer printing data of all the pixels on every row image to 256 color levels, and transmit the 256 color levels to the thermal print head 256 times sequentially. Then, the thermal print head will perform a printing operation 256 times according to the 256 color levels, in order to complete the printing procedure of the row image. During the above-mentioned printing operation, quite a large amount of color levels are required to be transmitted between the controlling circuit and the thermal print head. The transmission operation of these color levels not only costs time, but also results in more loadings on the firmware control of the thermal transfer printer, and further affects the whole printing efficiency of the thermal transfer printer.